CHANGELOG: add NVMe E2E and VFIO PCI support

  - Added hardware SGL support, which enables use of scattered buffers that

   don't conform to the PRP list alignment and length requirements on supported

   NVMe controllers.

  - Added end-to-end data protection support, including the ability to write and

  read metadata in extended LBA (metadata appended to each block of data in the

  buffer) and separate metadata buffer modes.

  See `spdk_nvme_ns_cmd_write_with_md()` and `spdk_nvme_ns_cmd_read_with_md()`

  for details.

- IOAT

  - The DMA block fill feature is now exposed via the `ioat_submit_fill()`

  function.  This is functionally similar to `memset()`, except the memory is

  filled with an 8-byte repeating pattern instead of a single byte like memset.

- PCI

  - Added support for using DPDK for PCI device mapping in addition to the

  existing libpciaccess option.

  existing libpciaccess option.  Using the DPDK PCI support also allows use of

  the Linux VFIO driver model, which means that SPDK userspace drivers will work

  with the IOMMU enabled.  Additionally, SPDK applications may be run as an

  unprivileged user with access restricted to a specific set of PCIe devices.

  - The PCI library API was made more generic to abstract away differences

  between the underlying PCI access implementations.